1. Field of the Invention
The present invention relates to a digitally switched analog signal conditioner and, more particularly, to a precision signal conditioner that can be constructed with imprecise active components and which permits a wide range of precision analog signal conditioning to be achieved, including multiplication, division, addition, subtraction, differentiation and integration using switched or clocked capacitor techniques.
2. Description of the Prior Art
Signal conditioning circuits are generally built around amplifiers and, heretofore, accurate amplifiers of the type for use in precision signal conditioners took the form of an operational amplifier or an instrumentation amplifier. The instrumentation amplifier is the most universal of amplifiers in that it will accept either a single ended input signal or a differential input signal and will amplify, divide, or condition this input signal, referencing the output signal (if so desired) to another reference voltage level, irrespective of the input signal levels. The reference voltage level may be system ground, or an independent reference voltage, or either input voltage.
Because of the above characteristics, instrumentation amplifiers are highly useful. On the other hand, they are difficult to build and costly. A typical instrumentation amplifier uses three operational amplifiers with very accurately matched resistors. The multiple operational amplifiers and the necessity to accurately match the bias resistors is what results in the difficulty to build instrumentation amplifiers and their cost.
An operational amplifier, on the other hand, is much more simple to build and far less costly. However, an operational amplifier must usually process an input signal with respect to a voltage which is common to both the input and the output. This prevents isolation between the input and the output of the operational amplifier. Consequently, the operational amplifier may be considered to be a special case of an instrumentation amplifier where the reference voltage level is one of the input voltage levels.
Switched capacitor systems are currently being used for comparators. See, for example, copending application Ser. No. 434,893, filed Oct. 18, 1982, entitled High Speed Charge Balancing Comparator and assigned to Intersil, Inc., the assignee of the present application. Switched capacitor systems are also being used in filter systems to provide the equivalent of resistors. However, in most switched capacitor filter regulators, operational amplifiers are used to provide the gain blocks. Switched capacitor amplifiers have not been used heretofore in general purpose analog signal conditioning circuits.